The card is listed with the dimensions of 12.9 x 9.5 x 2.9 inches. Having looked inside the case I'm worried that this card won't fit. Can anyone help me out with whether this card will fit in an XPS 8700 case?

As an aside, I am aware of UEFI compatibility issues with the 8700 and have already purchased a beefier power supply for a new card.

Dell XPS 8700 was never tested with the EVGA 4GB GeForce GXT 770. However, few users have successfully installed nVIdia GeForce GTX 770 2GB on their XPS 8700. Dimension of nVIdia GeForce GTX 770 2GB is 10.3" x 4.3" x Dual Slot. Hence before purchasing the card, I would suggest you to take the computer to a local store and check if the graphics card work on the system.

Dell XPS 8700 was never tested with the EVGA 4GB GeForce GXT 770. However, few users have successfully installed nVIdia GeForce GTX 770 2GB on their XPS 8700. Dimension of nVIdia GeForce GTX 770 2GB is 10.3" x 4.3" x Dual Slot. Hence before purchasing the card, I would suggest you to take the computer to a local store and check if the graphics card work on the system.

Amazon is notorious for having inaccurate video card dimensions. The GTX 770 you linked is only 10.5" long and about 4.4" high (standard). It takes one 6-pin and one 8-pin power connector. Therefore, it should fit fine if you don't have a 2nd hard drive in the lower bay. See the correct size HERE or you can even verify it on EVGA's website by downloading the spec sheet.

Note that 12.9 x 9.5 x 2.9 inches is the size of the box not the video card.

It works great, and Kelbear1 is correct, both cards are 10.5 inches long.

Naturally I upgraded my PSU to an OCZ ModXStream Pro 700W Modular High Performance Power Supply.

The real pain was reinstalling Windows on the SSD, I bought from Dell, but Dell support was very helpful in providing me with Windows reinstallation disks, and this PowerDVD disk to get my DVD playing movies.

You CAN probably have a second HD in the lower drive bay, I have one there.

240 GB SSD, and a 1 TB HD right below.

My mother board still has plug ins for 2 additional drives, and there is plenty of room in the bay for another SSD below the one I have in.

There also seems to be an additional bay for another HD off to the side, behind the main drive bays, and plenty of room below the DVD drive if you have to use that space.

If you can find a 4 GB Superclocked 780 TI, I would recommend it, over the 3 GB Superclocked 780 TI (1007 base clock) model I bought.

My card is very fast, and can play Bioshock Infinite, at 240-400+ FPS, with v-sinc off.

If you want to look at the blank sky it will go over 500 FPS, but it gets a bit loud if your turn off V-sinc. With V-sinc on it just purrs like a kitten, at 60 or 120 FPS. if you want to play in 3D (120 FPS).

The 780 TI is ridiculously powerful, and the XPS 8700 will only hold one GPU.

V-sinc limits your graphics card to the speed of your monitor.
If you have a 60 Hz monitor, it will output at 60 frames per second.
If you want to play games in 3D, then you need a 120 Hz moniter, and special glasses where the lenses blank out left and right lenses at 120 Frames per second.
If your turn it off, then your graphics card runs as fast as it can. With a 780 TI running Bioshock Infinite you will see frame rates of 240-400 frames per second, and over 500 frames per second if you look at the blank sky.
I don't know of any monitor that can handle that frame rate, so your graphics card is getting really noisy trying to keep itself cool (fan noise), and your monitor can't display at that speed, so you are burning up a lot of GPU power for nothing.
You just turn of V-sinc for bragging rights basically. There is no practical advantage to it.

For anyone wondering, I did go ahead and buy a GTX 780 shortly after making this thread. It worked great for me after addressing the UEFI compatibility issues. I had no problem fitting it into the XPS 8700. My games run great, I've got an Asus VG24QE 144hz monitor and can't wait until the G-sync do-it-yourself kit gets released.

Are you running windows 8.1? I am planning to get a GTX 760 2GB but I hear that there are problems with secure boot since I was just planning to uninstall NVidia drivers remove the card and just put the 760 in.

I had to disable "Secure boot" in the BIOS when I upgraded the 645 OEM card, first to a SC 660, and also later to the SC 780 TI.
You just press F2 or F12 or something when it boots up, and disable secure boot BEFORE you install the new card. If you do NOT, your computer will just beep 5 times, and NOT boot up. Then you will have to reinstall the OEM card, to get it to boot, disable "secure boot", then reinstall the new card.
I am also running Windows 8.1 64 bit (non-Pro). I'm not positive that the GTX 760 will not boot up with "secure boot" enabled, I never had one, but I would suspect that to be the case.
It's really not a big deal to try it either way, just so you understand what the problem is and how to solve it if your computer, beeps 5 times and will not boot up.

I'm not really sure what he means, but there are 3 cables that come from the motherboard that have to be routed around the GPU, in a standard XPS 8700. You can route them any way you want, in front of the GPU, behind it, or around the back of it.
You may need to order longer cables. Not from the power supply which sits above the GPU, but from the motherboard to your drives....SATA cables. I think they are called.
Since I have an additional SSD, I have 4 cables total routed around my GPU (Nvidia 780 TI).
Two around the back side, one around the front side, and one behind the GPU.
One cable goes to my SSD, one to my hard drive, one to my DVD, and one I don't remember where it goes to.
You are probably going to need a beefier power supply for a 770.
I don't really know, I'm no expert.
...but I did manage to put a 700 watt PSU and an Nvidis 780 TI in an XPS 8700.
I think the fellow just recommends you make sure your SATA cable to your hard drive is long enough. I had to get a longer one. The DVD cable is long enough, don't worry about that.
Good luck with your computer.